Modals of obligation and necessitySummary

Info. taken from Grammar for FCE (Hashemi and Thomas)

by Miss M. Eugenia2015

III MEDIO ADV.

For the test, you need to make sure you understand these things:

• The difference between needn’t have + past participle and didn’t need to + infinitive to talk about past events.

• The difference between mustn’t, have to and should to talk about obligation.

• The difference between mustn’t and don’t have to to talk about prohibition and things you don’t need to do.

If you understand all of these, relax!!!!!!!

Modal verbs

Although there are other modal verbs you can use to express obligation and necessity, we’ll only see these four:

1. Obligation

must

have to

should

2. Necessity

need

1. Obligation: mustWhen do we use it?

orders strong advice

PAST TENSE

No!

PRESENT TENSE

must + infinitive

FUTURE

No!

You must see her now!

1. Obligation: have toWhen do we use it?

rules habits

PAST TENSE

had to + infinitive

PRESENT TENSE

have to + infinitive

FUTURE

will have to + infinitive

I have to work to pay for my tickets.

Last year, I had to work extra hours to pay for this house.

I will have to train every day for next year’s marathon.

1. Obligation: shouldWhen do we use it?

talk about the right thing to do

PAST TENSE

should + have + past participle

PRESENT TENSE

should + infinitive

FUTURE

No

You should always carry your ID card in case

something happens to you.

You should have mentioned that you were the President’s daughter.

1. Obligation: ‘mustn’t’ or ‘don’t have to’?

mustn’t

mustn’t + infinitive

don‘t have to

don‘t/doesn’t have to + infinitive

It means ‘don’t do it!’ It means ‘it’s not necessary to do it.’

For example:I know you don’t like visiting

your uncle. So, you don’t have to come if you don’t want to.

You mustn’t drive over 70mph on the roads in Britain.

It’s like… ‘I’m not asking you not to do that. I’m serious. DON’T DRIVE OVER THAT SPEED LIMIT! It’s forbidden, unless you want to spend your vacations in jail.’

It’s like ‘OK. You’re being a terrible nephew, but your kind mother is giving you the chance to choose whether you want to go or not. Maybe you might not receive any presents from your uncle for Christmas though. Your choice.’

Wanna try? Here you have some exercises: (ANSWER KEY next slide)

ANSWER KEY

2. Necessity: need to/needPAST TENSE

(+) needed to + inf.

(-) didn‘t need to + inf.

(-) needn’t have + past participle

PRESENT TENSE

(+) need to + inf.

(-) don’t/doesn’t need to +

(-) needn’t + inf.

(?) Do I need to + inf.

(?) Need I + inf.

FUTURE

will need to + inf.

I needed to know who the person was. Now, I can

forget about it.

This means the person can rest in peace and let it go (just like Frozen) because he/she already knows what he needed to know. The past is in the past.

2. Necessity: need to/needPAST TENSE

(+) needed to + inf.

(-) didn‘t need to + inf.

(-) needn’t have + past participle

PRESENT TENSE

(+) need to + inf.

(-) don’t/doesn’t need to +

(-) needn’t + inf.

(?) Do I need to + inf.

(?) Need I + inf.

FUTURE

will need to + inf.

I need to know who the person is. I won’t rest until I find out who murdered

my father.

This may sound familiar (yeah, Hamlet). So, the person still doesn’t know the information and it’s a necessity for him/her to know it. That’s why it’s present tense.

2. Necessity: need to/needPAST TENSE

(+) needed to + inf.

(-) didn‘t need to + inf.

(-) needn’t have + past participle

PRESENT TENSE

(+) need to + inf.

(-) don’t/doesn’t need to +

(-) needn’t + inf.

(?) Do I need to + inf.

(?) Need I + inf.

FUTURE

will need to + inf.

I needn’t know who murdered my father. I’m

OK.

Let’s imagine a ‘more relaxed’ Hamlet…

I don’t need to know who

murdered my father. I’m OK.

OR

2. Obligation: needn’t have + past participle or didn’t need to?

needn‘t + have + past participle

didn‘t need to + infinitive

It means ‘someone did something that wasn’t

necessary’

It means ‘someone didn’t do it as it wasn’t necessary’

In both cases, we’re talking about something that happened in the past. The only difference is that in one case we did something that wasn’t necessary to do, and in the second case we were going to do it but in the end we didn’t since it wasn’t necessary.

For example:My father put the dishes in the dishwasher so I didn’t need to

wash them.

You needn’t have washed the dishes. I would have put them

in the dishwasher.

It’s like… ‘DUH, you spent your precious time washing the dishes when it wasn’t necessary because a machine was going to do it for you.’

It’s like ‘Yeah, I’m too cool for you. I didn’t wash the dishes because someone else (in this case something else) did it for me.’